Theory of pressure solution by indentation and in porous solids

Abstract

The principles underlying the water enhanced deformation of rocks by diffusive mass transfer (pressure solution) have been known since the work of Sorby in 1863, and extensive field evidence has accumulated which confirms the prevalence of this mechanism in nature. Attempts to reproduce the mechanism and to obtain quantitative information in the laboratory have proved difficult however, owing to incomplete analysis of geometries used in experimental study and to the confounding influence of other deformation mechanisms that can operate concurrently in the experiments. In the present work, new analyses of pressure solution are presented. First, analyses are given for indentation tests that may provide experimental verification of the mechanism. These rely on evaluation of the penetration velocity of indentors having various geometries. The treatment for a hollow indentor leads naturally to the problem of the pressure solution of a porous solid. The influence of porosity on overall deformation rate is considered. There are striking geometrical and mathematical similarities between pressure solution, which occurs by solute diffusion along an aqueous film, and certain processes that occur by interfacial vacancy diffusion in crystalline solids. These are indentation creep, the diffusive movement of inclusions, and grain boundary diffusion creep. These are considered in an appendix.